JP2003297780A - Method for manufacturing mirror surface semiconductor wafer, method for producing abrasive slurry for semiconductor wafer, and abrasive slurry for semiconductor wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase the production yield of semiconductor device surely by making clear a mechanism where a contaminant metal in abrasive is diffused into a silicon wafer during a polishing operation thereby determining parameters for lowering the contamination of the silicon wafer down to a predetermined level or below. <P>SOLUTION: At the time of producing abrasive slurry 1, an alkali being added is conditioned such that the concentration of copper becomes 0.2 ppb or less. Furthermore, the quantity of alkali being added is regulated such that the pH of the abrasive slurry 1 falls in a range of 10.2-10.6. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a mirror-like semiconductor wafer by polishing the surface of a semiconductor wafer such as a silicon wafer, a polishing slurry for a semiconductor wafer used for polishing the surface of a semiconductor wafer, and this semiconductor wafer. The present invention relates to a method of manufacturing a polishing slurry for use in manufacturing.

[0002]

2. Description of the Related Art In each of the steps for manufacturing a silicon wafer, in the polishing step (polishing step), the surface of the silicon wafer is mirror-polished using a polishing slurry.

As shown in FIG. 2, the polishing slurry 1 generally comprises silica (Si) having a particle size of about 30 to 200 nm.
O ₂ ) particles (abrasive grains) 2 with a pH of about 10 to 11
It is colloidally dispersed in an alkaline aqueous solution 3 such as OH or KOH.

In the polishing process, the polishing slurry 1 is supplied between the silicon wafer and the polishing pad. Then, by pressing the silicon wafer against the polishing pad and rotating the silicon wafer and the polishing pad respectively, the surface of the silicon wafer is mirror-polished. The polishing step is divided into a primary polishing step of flattening the wafer surface at high pressure and high speed, and a final polishing step of removing the haze of the wafer after the primary polishing to finish it into a mirror surface. The polishing slurry 1 is used in the primary polishing process.

Polishing using the polishing slurry 1 is performed by "mechanochemical polishing". That is, the silica particles as abrasive grains mechanically act on the surface of the silicon wafer to scrape the surface, and the alkaline solution 3 chemically reacts on the surface of the silicon wafer to dissolve the surface.

The polishing slurry 1 contains a contaminant metal. Types of contaminant metals include copper (Cu), nickel (Ni), chromium (Cr), iron (Fe), and the like. Contaminating metals such as copper and nickel can be converted from natural quartz to silica particles 2
It is introduced as an impurity from the outside in the process of manufacturing.

Polishing slurry 1 containing such contaminant metals
When a silicon wafer is polished by using, the contaminant metal diffuses into the bulk of the silicon wafer during the polishing process and deteriorates the quality of the silicon wafer. When a semiconductor device is manufactured using such a silicon wafer having deteriorated quality, the yield of the semiconductor device is adversely affected. Among the contaminating metals, copper has the highest diffusion rate in the silicon wafer, so that it rapidly penetrates deeply into the silicon wafer during the polishing process, and has a great adverse effect on the yield of semiconductor devices. For example, when a silicon wafer is polished using a polishing slurry 1 containing copper of about 5 ppb, the amount of copper contamination (atoms / cm ² ) diffused in the silicon wafer is 10 ⁹ to 10 ¹⁰ atoms / cm ^2.
, Which has a great adverse effect on the yield of semiconductor devices. Here, the amount of contamination (atoms / cm ² ) is evaluated by the number of atoms per unit area of contaminated metal deposited on the wafer surface when a mirror-finished silicon wafer is stored for a long time (for example, 3 months). .

Therefore, conventionally, there has been considered a method of reducing the concentration of the contaminant metal in the polishing slurry 1 to such an extent that the yield of semiconductor devices is not adversely affected.

As a method of reducing the concentration of the pollutant metal in the polishing slurry 1, it is conceivable to remove the pollutant metal by spending time and cost in the refining process in the manufacturing process of the polishing slurry 1. Certainly, the more time and cost it takes to purify, the lower the concentration of contaminant metals such as copper, but the work efficiency is poor and it is not realistic.

Therefore, in JP-A-11-186201, the concentration of copper and nickel in the polishing slurry is kept in the range of 0.01 to 1 ppb by a cation exchange resin, and the amount of sodium hydroxide aqueous solution added is adjusted. The invention discloses that the amount of contamination of copper and nickel diffused in a silicon wafer during polishing is reduced by controlling the pH of the polishing slurry to 11 or less.

[0011]

However, according to the findings of the present inventors, "copper in polishing slurry,
The parameter and the range that the total concentration of nickel is 0.01 to 1 ppb and the pH of the polishing slurry is 11 or less "are required to keep the amount of contamination of copper and nickel diffused in the silicon wafer during the polishing process below a certain level. It has become clear that the yield does not decrease to a satisfactory level for semiconductor device yields.

The present invention clarifies the mechanism by which the contaminant metal in the polishing slurry diffuses into the silicon wafer during the polishing process, and clearly defines the parameters for reducing the contaminant amount of the silicon wafer below a certain level, and The problem to be solved is to surely improve the manufacturing yield of the above.

[0013]

[Means for Solving the Problems and Effects] The first invention is
In the method of manufacturing a mirror-like semiconductor wafer, an alkali is added to an undiluted slurry solution to produce a polishing slurry, and the surface of the semiconductor wafer is polished with this polishing slurry to produce a mirror-like semiconductor wafer. So that the amount of polluted metal that is generated is below a certain level,
It is characterized in that a semiconductor wafer is polished using a polishing slurry to which an alkali having a concentration of contaminant metals of 0.2 ppb or less is added for each metal species.

A second aspect of the present invention is a method for producing a mirror-like semiconductor wafer, in which an alkali is added to an undiluted slurry solution to produce a polishing slurry, and the surface of the semiconductor wafer is polished with this polishing slurry to produce a mirror-like semiconductor wafer. , So that the amount of the contaminant metal deposited on the surface of the mirror-polished semiconductor wafer is below a certain level, an alkali having a concentration of the contaminant metal of 0.2 ppb or less is added for each metal species, and the pH is 10. It is characterized in that a semiconductor wafer is polished by using a polishing slurry adjusted within a range of 2-10.6.

A third invention is characterized in that, in the first invention or the second invention, the polishing slurry contains silica particles.

A fourth aspect of the present invention is a method for producing a polishing slurry for a semiconductor wafer, in which an alkali is added to an undiluted slurry solution to produce a polishing slurry used for polishing a semiconductor wafer. The method is characterized by including the step of adding an alkali having a concentration of the contaminating metal of 0.2 ppb or less for each metal species so that the amount of the metal is below a certain level.

A fifth aspect of the present invention is a method for producing a polishing slurry for a semiconductor wafer, which is for producing a polishing slurry used for polishing a semiconductor wafer by adding an alkali to an undiluted slurry solution. To keep the amount of metal below a certain level, add an alkali whose concentration of contaminating metal is less than 0.2 ppb for each metal species and adjust the pH to 10.2-10.6.
It is characterized by including a step of adjusting within the range.

A sixth invention is characterized in that, in the fourth invention or the fifth invention, the polishing slurry contains silica particles.

A seventh aspect of the present invention is a polishing slurry for semiconductor wafers, which is manufactured by adding an alkali to a slurry stock solution and is used for polishing semiconductor wafers, wherein the amount of contaminant metal deposited on the surface of a mirror-like semiconductor wafer is large. Is a polishing slurry for semiconductor wafers, in which an alkali having a concentration of contaminating metal of 0.2 ppb or less for each metal species is added so that the concentration becomes below a certain level.

An eighth aspect of the present invention is a polishing slurry for semiconductor wafers, which is produced by adding an alkali to an undiluted slurry solution and is used for polishing semiconductor wafers. So that the concentration of pollutant metal is 0.2 ppb or less for each metal species, p
It is a polishing slurry for semiconductor wafers, wherein H is adjusted within the range of 10.2 to 10.6.

A ninth invention is characterized in that, in the seventh invention or the eighth invention, it is a polishing slurry for semiconductor wafers containing silica particles.

Main first invention, fourth invention, and seventh invention of the present invention
In the present invention, when the polishing slurry 1 is manufactured, the alkali added is adjusted so that the copper concentration is 0.2 ppb or less.

The second, fifth inventions, which are the main features of the present invention,
In the eighth invention, when the polishing slurry 1 is manufactured, the alkali to be added is adjusted so that the concentration of copper is 0.2 ppb or less, and the addition amount of the alkali is adjusted to adjust the amount of the polishing slurry 1. Adjust the pH so that it falls within the range of 10.2-10.6.

When a silicon wafer was polished using the polishing slurry 1 thus manufactured and a semiconductor device was manufactured using a mirror-finished silicon wafer, the manufacturing yield was at a satisfactory level.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments will be described below with reference to the drawings. In this embodiment, a silicon (Si) wafer is assumed as a semiconductor wafer, but the embodiments described below are applicable to gallium arsenide wafers other than silicon wafers. Further, in the present embodiment, copper (Cu) is assumed as the polluting metal, but it is also applicable to contaminating metals such as nickel (Ni), chromium (Cr), iron (Fe) other than copper. In particular, nickel has a high diffusion rate in a silicon wafer like copper, and therefore can be treated like copper in the following embodiments.

In the polishing step (polishing step) of the respective steps of manufacturing a silicon wafer, the surface of the silicon wafer is mirror-polished using a polishing slurry.

First, the knowledge of the present invention will be described with reference to FIGS. FIG. 2 shows the components of the polishing slurry 1 of the embodiment, in which silica (SiO ₂ ) particles (abrasive particles) 2 having a particle diameter of about 30 to 200 nm are colloidal in an alkaline aqueous solution 3 such as NaOH or KOH. It is dispersed.

Copper in the polishing slurry 1 is divided into the following three types.

1) Copper 4a contained inside the silica particles 2) Copper 4b attached to the surface of the silica particles 2 due to the charge on the surface 3) Copper ions 4c present in the alkaline aqueous solution 3 Among the three types of copper 4a, 4b, and 4c, the above-mentioned 1) "copper 4a contained in the silica particles 2" has the largest amount. However, the amount of copper that penetrates into the silicon wafer and diffuses inside during the polishing process, that is, the amount of contamination is determined by the amount of “copper ions 4c existing in the alkaline aqueous solution 3” in 3) above. In other words, the copper 4a in the polishing slurry 1,
Even if the total concentration of 4b and 4c is higher than 1 ppb, if the concentration of copper ions 4c is low, the contamination amount of the silicon wafer is low. On the contrary, even if the total concentration of the copper 4a, 4b, 4c in the polishing slurry 1 shows a low value of 1 ppb or less, if the concentration of the copper ions 4c is high, the contamination amount of the silicon wafer shows a high value.

What is present in the alkaline aqueous solution 3 is mostly copper hydroxide {Cu (OH) ₂ , Cu in the alkaline aqueous solution 3 having a pH of 10 to 11.
₂ O}, Cu ²⁺ ions and Cu (OH) ₄ ²⁻ /
Only a very small number of HCu (OH) ₄ ⁻ ions are present.

During polishing, the surface of the silicon wafer is
Since it is negatively charged, Cu (OH)_Four ^2-/ HCu (O
H)_Four ⁻Ion and Cu²⁺When compared with ION, it is positive
Cu ²⁺Ions are adsorbed on the surface of the silicon wafer
And easily diffuse inside the silicon wafer. others
To reduce the amount of copper contamination on silicon wafers,²⁺
It is important to reduce the number of ions.

Further, the copper ions 4c contained in the polishing slurry 1 are divided into the following four types.

3-1) Copper ion 4c1 contained in the undiluted slurry 3-2) Copper ion contained in pure water for dilution 4c2 3-3) Copper ion contained in the alkali to be added Four
c3 3-4) In addition, copper ions 4c4 eluted from the polishing pad or the piping of the device, etc. It turns out that the following relationship is established.

Generally, an alkali is added to a general-purpose slurry stock solution to adjust the polishing slurry 1 to a desired composition. Therefore, rather than adjusting the amount of copper ions 4c1 in the stock slurry solution, copper in the added alkali stock is adjusted. It is easier to adjust the amount of the ions 4c3. If a high-purity alkali is used as the added alkali, the concentration of copper can be reduced, and as a result, the amount of copper ions 4c3 can be reduced.

The present inventors have also found that the presence state of ions also changes depending on the pH of the polishing slurry 1.

That is, when the pH is high, Cu (OH) ₄
²⁻ / HCu (OH) ₄ ⁻ ions increase and Cu ²⁺ ions decrease. Conversely, if the pH is low, Cu (OH) ₄ ²⁻ /
HCu (OH) ₄ ⁻ ions decrease and Cu ²⁺ ions increase.

The surface state of the mirror-finished silicon wafer after polishing also changes depending on the pH of the polishing slurry 1. That is, when the pH is high, the charge amount on the surface of the silicon wafer increases, the polishing rate increases, the charge amount of the silica particles 2 increases, and the processing temperature decreases. On the other hand, when the pH is low, the charge amount on the surface of the silicon wafer decreases, the polishing rate decreases, the charge amount of the silica particles 2 decreases, and the processing temperature increases.

In FIG. 1, the horizontal axis represents the pH of the polishing slurry 1 and the vertical axis represents the mirror surface silicon wafer polished by using the polishing slurry 1 when deposited on the wafer surface for a long time (for example, 3 months). Area density of copper (atoms / cm ² )
Is taken. That is, the vertical axis represents the amount of copper contamination diffused in the silicon wafer.

The characteristic L1 indicated by the solid line in FIG. 1 is that the purity of the added alkali is high and the concentration of copper contained is 0.2.
The characteristics are shown when an alkali of ppb or less is added. The characteristic L2 indicated by the one-dot chain line shows the characteristic when the alkali added has a low purity and the concentration of copper contained is higher than 0.2 ppb. The copper concentration is shown as the concentration in a 10% aqueous solution.

As shown in FIG. 1, when an alkali having a high purity and a copper concentration of 0.2 ppb is added, when the pH of the polishing slurry 1 is 10.2 or more and 10.6 or less, The amount of copper contamination on silicon wafers is minimal. Even if the alkali purity is further increased and the copper concentration is further reduced to less than 0.2 ppb, the same tendency is exhibited.

As described above, when the pH is high, Cu (O
H) ₄ ²⁻ / HCu (OH) ₄ ⁻ ions increase, and Cu
^From the knowledge that " ²⁺ ions decrease", Cu2 ⁺ ions that contribute to the contamination of the silicon wafer should decrease as the pH increases. However, if the pH is too high, the dissolution of the silica particles 2 will proceed, and the copper 4a inside the silica particles 2 will dissolve in the alkaline aqueous solution 3, resulting in a large amount of copper ions 4c (Cu ²⁺ ions). I will end up. Therefore, there is an optimum pH range of 10.2 to 10.6 for reducing the amount of copper contamination of the silicon wafer.

However, as shown in the characteristic L2, when the alkali purity is lowered and the copper concentration is higher than 0.2 ppb, "10.
When it is 6 or less, the amount of copper contamination of the silicon wafer becomes minimum ”. Therefore, if an alkali having a high purity (an alkali having a copper concentration higher than 0.2 ppb) is used, it is desirable that the pH of the polishing slurry 1 be as low as possible, as is well known.

As described above, an alkali having a copper concentration of 0.2 ppb or less was added, and the pH of the polishing slurry 1 was 10.2.
When adjusted to the range of ˜10.6, it was possible to suppress the amount of copper contamination of the silicon wafer 1 and bring the yield of semiconductor device manufacturing to a satisfactory level. Further, in FIG. 1, the copper contamination amount of the silicon wafer is 1.0 × 10 ⁸ (atom
Since it is below the measurement limit when it is s / cm ² ) or less, reduce the concentration of copper in the added alkali so that the copper contamination amount of the silicon wafer is 1.0 × 10 ⁸ (atoms / cm ² ) or less. Is desirable.

However, the pH of the polishing slurry 1 is generally 10
~ 11, so the pH is not always 10.2-1
It is also possible to adjust the concentration of copper in the added alkali to 0.2 ppb or less without adjusting it to the range of 0.6.

The polishing slurry 1 in which the concentration of the ionized copper 4c is reduced is specifically manufactured as follows.

That is, the silica particles 2 are colloidal 30
An alkaline slurry stock solution containing wt%, pure water for dilution, and an alkali such as NaOH or KOH are prepared.

Therefore, the slurry stock solution is diluted with 10 times or more (about 10 to 20 times) pure water, and alkali is further added to produce the polishing slurry 1.

The alkali added here was adjusted so that the copper concentration was 0.2 ppb or less.

The amount of alkali added was adjusted so that the pH of the polishing slurry 1 was in the range of 10.2 to 10.6. The pH of the polishing slurry 1 is about 10 when no alkali is added.

Copper 4 in the polishing slurry 1 thus produced
The total atomic amount of a, 4b, and 4c is about 1 to 10 ppb. However, the copper ion 4c is remarkably reduced.

In the silicon wafer polishing step, the polishing slurry 1 manufactured as described above is supplied between the silicon wafer and the polishing pad. Then, by pressing the silicon wafer against the polishing pad and rotating the silicon wafer and the polishing pad respectively, the surface of the silicon wafer is mirror-polished.

When a semiconductor device was manufactured using the mirror-finished silicon wafer manufactured in this manner, the manufacturing yield was at a satisfactory level.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the pH of polishing slurry and the areal density of copper deposited on the surface of a silicon wafer after long-term storage.

FIG. 2 is a diagram showing components of polishing slurry, and is a diagram for explaining a mode of existence of copper.

[Explanation of symbols]

1 polishing slurry 2 Silica particles 3 alkaline aqueous solution 4a, 4b Copper 4c Copper ion

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Akira Nishi             3-25-1, Shinomiya, Hiratsuka, Kanagawa Prefecture             Matsu Electronics Co., Ltd. (72) Inventor Masato Imai             3-25-1, Shinomiya, Hiratsuka, Kanagawa Prefecture             Matsu Electronics Co., Ltd. F-term (reference) 3C047 FF08 GG20                 3C058 AA07 CA01 CB03 CB05 DA02                       DA12

Claims (9)

[Claims] 1. A mirror surface semiconductor wafer manufacturing method for manufacturing a polishing slurry by adding an alkali to an undiluted slurry solution to manufacture a polishing slurry, and polishing the surface of a semiconductor wafer using the polishing slurry. Polishing a semiconductor wafer with a polishing slurry containing alkali with a concentration of pollutant metal of 0.2 ppb or less for each metal type so that the amount of pollutant metal deposited on the surface of the wafer falls below a certain level. A method for manufacturing a mirror-like semiconductor wafer, comprising: 2. A mirror surface semiconductor wafer manufacturing method for manufacturing a mirror surface semiconductor wafer by manufacturing a polishing slurry by adding an alkali to an undiluted slurry solution and polishing the surface of a semiconductor wafer using the polishing slurry. An alkali having a concentration of the pollutant metal of 0.2 ppb or less for each metal species is added so that the amount of the pollutant metal deposited on the surface of the wafer is below a certain level, and the pH is 10.2 to 10.6. A method for producing a mirror-like semiconductor wafer, which comprises polishing a semiconductor wafer by using a polishing slurry adjusted within the range. 3. The polishing slurry according to claim 1, wherein the polishing slurry contains silica particles.
A method for manufacturing a mirror-like semiconductor wafer according to claim 1. 4. A method for producing a polishing slurry for a semiconductor wafer, which comprises producing a polishing slurry used for polishing a semiconductor wafer by adding an alkali to an undiluted slurry solution, the amount of a contaminant metal deposited on the surface of a mirror-finished semiconductor wafer. So as to be below a certain level, a method for producing a polishing slurry for semiconductor wafers, comprising the step of adding an alkali having a concentration of contaminating metal of 0.2 ppb or less for each metal species. 5. A method for producing a polishing slurry for a semiconductor wafer, which comprises producing a polishing slurry used for polishing a semiconductor wafer by adding an alkali to an undiluted slurry solution, the amount of a contaminant metal deposited on the surface of a mirror-finished semiconductor wafer. So that the concentration is below a certain level, add an alkali with a concentration of pollutant metal of 0.2 ppb or less for each metal species,
And the manufacturing method of the polishing slurry for semiconductor wafers characterized by including the process of adjusting pH to the range of 10.2-10.6. 6. The polishing slurry according to claim 4, wherein the polishing slurry contains silica particles.
A method for producing a polishing slurry for a semiconductor wafer according to claim 1. 7. A polishing slurry for a semiconductor wafer, which is produced by adding an alkali to a slurry stock solution and is used for polishing a semiconductor wafer, wherein the amount of contaminant metal deposited on the surface of a mirror-like semiconductor wafer is constant. As described below, a polishing slurry for semiconductor wafers, wherein an alkali having a concentration of a contaminant metal of 0.2 ppb or less for each metal species is added. 8. A polishing slurry for a semiconductor wafer, which is produced by adding an alkali to an undiluted slurry solution and is used for polishing a semiconductor wafer, wherein the amount of contaminant metal deposited on the surface of a mirror-like semiconductor wafer is constant level. A semiconductor wafer characterized in that an alkali having a concentration of a pollutant metal of 0.2 ppb or less is added to each metal species and the pH is adjusted within the range of 10.2 to 10.6 as follows. Polishing slurry for. 9. The polishing slurry for semiconductor wafers according to claim 7, which contains silica particles.